The present invention relates generally to a compression piston switch. More specifically, the present invention relates to a switch having two relatively displaceable switching parts and also having a device, connected to one of the parts, for guiding a quenching gas flow.
Such a switch has been disclosed in German Auslegeschrift No. 2,039,240. In this switch, a nozzle connected to the first switching part is provided in a region of a nozzle constriction with a graphite part of annular construction. The graphite part is electrically conductively connected to a main contact, constructed as a tubular shell, of the second switching part. The graphite part is designed to accept the root of an arc drawn between the switching parts, when they are being disconnected, as soon as the distance between the switching parts attains a predetermined value. Since the arc is then burning between the nozzle and the switching part connected to the nozzle, the distance between the arc roots remains constant. This is intended to prevent an unnecessary elongation of the arc and also to increase the switching capacity.
In this arrangement, however, the electric field generated after quenching of the arc in the zero transition of the current, as a result of the voltage returning in the quenching zone located between the switching parts, is pushed into the section of the compression space located between the nozzle and the first switching part. This section, although subjected to high pressure, is nevertheless constructed to be narrow and is subjected to a great thermal load. In addition, a high surface temperature is caused by the arc striking on the nozzle. The two phenomena lead to an impairment of the dielectric strengthening of the quenching zone.
It is a primary object of the present invention to create a switch of the generic type in which the dielectric strengthening of the quenching zone is increased by preventing to a large extent the compression of the field between the nozzle and the first switching part.
Accordingly, a compression piston switch according to the present invention includes two relatively displaceable switching parts and a device connected to the first of the switching parts for guiding a quenching gas flow. A quenching gas, used for quenching the switching arc, flows through at least one constriction from a compression space into an expansion space in which at least one flow-guiding annular part is provided. The annular part is electrically conductively connected to the first switching part.
The switch according to the present invention is distinguished by the fact that the breaking capacity, particularly in the short-circuit case and with opposed phases, is increased with respect to comparable known switches. In particular, flash-overs over insulating parts are eliminated since no insulating material surfaces occur which are loaded by a field. Dimensions and the arrangement of the parts determining the supply of fresh quenching gas from the compression space, such as inlet duct and nozzle constriction, can now be designed independently of dielectric considerations since these parts are not under the load of a field. Since the electric field is essentially determined by the shape of the annular part and shielding, the dielectric characteristics of the quenching zone can be optimized independently of the arc quenching characteristics. It is also advantageous that the nozzle constriction is not loaded by a field since it is located inside a capsule of conductive material.
By developing the switch according to the invention so that a cylindrical portion of insulating material is provided outside the annular portion, the flow relationship in the area between the second switching part and the constriction of the device can be influenced so as to guide the flow of the quenching gas. In this case, the insulating cylindrical portion is attached to the annular portion and has an axial extension which extends past the free end of the annular portion.
The advantages of other embodiments of the invention are apparent from the description which follows.